[ruby-core:94929] [Ruby master Feature#16166] Remove exceptional treatment of *foo when it is the sole block parameter

Issue #16166 has been updated by shevegen (Robert A. Heiler).


> We need an evidence that the behavior actually confuses
> many people, at least.

It does not confuse me because ... I try to avoid it altogether. :D

I think sawa's issue can be a bit shortened (sorry!) to the last
comparison:

    instance_exec(["a"]){|*foo| foo} # => [["a"]]
    instance_exec(["a"]){|*foo| foo} # => ["a"]

Although I may miss (or not completely understand) all of the reasoning,
I think that change would make sense (to me) - but I may not understand
the consequences.

I only remember even matz having fun in a presentation with the 
whole keyword arg situation before. ;) (One reason why I try to
actually avoid keywords is because I find them more difficult to
deal/cope with than oldschool options hash. But I guess this may
differ from ruby user to ruby user since it is a personal preference.)

Perhaps there should be a simple and consistent rule for how * and **
is to be interpreted at all times, including what should happen if
both are used at the same time. What I find indeed a bit confusing
is that * changes if ** is also used. That part is very strange to
me personally. Might also be mentioned in the documentation, but 
for me personally, I gladly stick to the simpler variants. :D

----------------------------------------
Feature #16166: Remove exceptional treatment of *foo when it is the sole block parameter
https://bugs.ruby-lang.org/issues/16166#change-81545

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
In the parameter signature of a code block for a method that is not involved in method definition or creation of lambda objects, two types of arguments `["a"]` and `"a"` are neutralized:

```ruby
instance_exec(["a"]){|foo, bar| foo} # => "a"
instance_exec("a"){|foo, bar| foo} # => "a"

instance_exec(["a"]){|*foo, **bar| foo} # => ["a"]
instance_exec("a"){|*foo, **bar| foo} # => ["a"]
```

This is the same behavior as with assignment constructions:

```ruby
foo, bar = ["a"]; foo # => "a"
foo, bar = "a"; foo # => "a"

*foo = ["a"]; foo # => ["a"]
*foo = "a"; foo # => ["a"]
```

And it contrasts with constructions involved in method definition or creation of lambda objects, where the distinction is preserved:

```ruby
lambda{|foo| foo}.call(["a"]) # => ["a"]
lambda{|foo| foo}.call("a") # => "a"

->(foo){foo}.call(["a"]) # => ["a"]
->(foo){foo}.call("a") # => "a"

lambda{|*foo| foo}.call(["a"]) # => [["a"]]
lambda{|*foo| foo}.call("a") # => ["a"]

->(*foo){foo}.call(["a"]) # => [["a"]]
->(*foo){foo}.call("a") # => ["a"]
```

However, when `*foo` is the sole parameter of a code block for a method that is not involved in method definition or creation of lambda objects, `["a"]` and `"a"` are not neutralized:

```ruby
instance_exec(["a"]){|*foo| foo} # => [["a"]]
instance_exec("a"){|*foo| foo} # => ["a"]
```

behaving in contrast to assignment constructions, and rather on a par with constructions involved in method definition or creation of lambda objects.

Particularly, existence or absence of another parameter `**bar` entirely changes what `foo` refers to:

```ruby
instance_exec(["a"]){|*foo| foo} # => [["a"]]
instance_exec(["a"]){|*foo, **bar| foo} # => ["a"]
```

I find this behavior inconsistent and confusing. I would like to request to remove this exceptional treatment of splatted parameter `*foo` when it is the sole parameter in a code block. I request this behavior:

```ruby
instance_exec(["a"]){|*foo| foo} # => ["a"]
```




-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>